The present invention is directed to a method for the storage stabilization of polyhydroxybutadienes (hydroxy-containing butadiene homopolymers). More specifically, the invention relates to stabilization from reactivity changes and especially increases in reactivity with isocyanates to prepare urethane compounds which may be used in the aerospace industry as a major component in the binder of solid propellant systems. Reactivity of the polyhydroxybutadienes increases over a period of time upon storage at ambient conditions. This increase is extremely undesirable and poses problems for the formulators because operating parameters must be periodically changed, resulting in additional expense. Furthermore, the urethane polymer obtained from the reaction may exhibit inferior physical properties compared to that prepared with a newly manufactured lot of polyhydroxybutadiene resin.
Various stabilizers, antioxidants, etc. have been proposed for incorporation into polyhydroxybutadiene compounds in attempts to prevent the reactivity changes upon ambient storage. Such additives include hindered phenols such as 2,2'-methylene bis (4-methyl-6-t-butyl phenol), substituted amines such as N-phenyl-N'-cyclohexyl-p-phenylenediamine and phosphites such as phenyldidecyl phosphite as well as combinations of the hindered phenol and phosphites mentioned above. All such additives have certain drawbacks in that they are either ineffectual, are not long lasting or will react with the isocyanate in the preparation of urethanes to introduce undesirable variations into the final urethane formulations.
It has now been discovered that polyhydroxybutadienes (hydroxy-containing butadiene homopolymers) can be effectively storage stabilized with long lasting effect by incorporating into the polymer resin a di or triphenylphosphine compound. The addition of the phosphine compound has the following advantages: (1) effectively prevents reactivity changes from occurring, (2) partially restores material to original reactivity after aging has taken place, (3) results in colorless solutions, (4) compounds are nonvolatile and (5) are nonreactive.
Applicants are not aware of any truly pertinent art that is deemed to be anticipatory or suggestive of the concept of the present invention.
It is therefore an object of this invention to provide a novel method for storage stabilizing polyhydroxybutadienes against reactivity changes when reacted with isocyanate compounds to prepare urethanes.
These and other objects and advantages of this invention will become apparent from the description of the invention which follows and from the claims.